Russian President Vladimir Putin has ordered more than 17,000 troops to withdraw from an area near the Ukrainian border as he prepares to meet with Ukraine's President Petro Poroshenko.

A Kremlin spokesman said the Russian troops spent the past few months training in the Rostov region, which is located across the border from the areas in southeastern Ukraine where pro-Russian rebels have been battling government forces.

Poroshenko said Saturday that he and Putin would hold talks later this week on the sidelines of an Asia-Europe summit in Milan.

The Ukrainian leader warned of difficult negotiations, while telling reporters the country was "very close" to settling a gas dispute with Moscow.

Russia shut off gas deliveries to energy-dependent Ukraine in June over what Moscow said were more than $5 billion in unpaid energy bills. The cutoff raises the specter of significant shortages in Kyiv and beyond, as the predictably harsh Eurasian winter approaches.

Ukraine defense minister resigns

Ukrainian President Petro Poroshenko accepted on Sunday the resignation of his embattled defense minister, Valery Heletey, who had been under criticism since August when Ukrainian forces suffered heavy losses at Ilovaysk, east of the main rebel-held eastern city of Donetsk.

Kyiv says more than 100 Ukrainian soldiers and members of volunteer battalions were encircled and killed in the Ilovaysk area in an unexpected attack by Russian forces supporting the separatists.

Poroshenko had appointed Heletey, a former head of a presidential bodyguard unit, only in July. He hopes to present a new candidate to parliament Monday.

Heletey, 47, drew criticism almost immediately after his appointment when he claimed Ukrainians would see a future victory parade in Crimea, the Black Sea peninsula Russia annexed in March.

Quieter on frontlines

Meanwhile, Ukraine defense spokesman Andriy Lysenko said attacks by pro-Russian separatists in Ukraine's embattled east appeared to be subsiding. Speaking Saturday in Kyiv, he said Ukraine forces were ready to withdraw heavy weaponry from the front where rebels and Ukrainian troops have battled for months.

Separately, rebel leader Oleksandr Zakharchenko told reporters in Donetsk that separatists could begin a similar frontline artillery withdrawal this week.